Starting arrangement for gyroscopic instruments



March 11, 1952 Q BARKALOWJ 2,588,607 7 STARTING ARRANGEMENT FOR GYROSCOPIC INSTRUMENTS Filed June 28, 1949 INVENTOR C1 AME E. Ba e/mam ATTORNEY Patented Mar. 11, 1952 STARTING ARRANGEMENT FOR GYROSCOPIC INSTRUMENTS Clare E. Barkalow, Huntington, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application June 28, 1949, Serial No. 101,770

8 Claims.

This invention relates to a starting arrangement for electrically operated gyroscopic instruments. The improved arrangement includes means that are effective during starting conditions to render ineffective the normally operable torque exerting means .normally used to level or erect the gyroscope. In accordance with the invention, such means is made sensitive to the current drawn by the motor adapted to spin the gyroscopic rotor of the instrument, the motor being of a character that draws a decreasing amount of electric current as the gyroscopic rotor accelerates from a standstill condition to reach normal operating speed. Upon arrival at the normal operating speed of the rotor, the means is effective to restore the torque exerting means to normal operation.

Particularly, in directional gyros, the levelling torque exerting means for the rotor frame adds to the starting nutation of the instrument as the gyroscopic rotor is brought up to speed. By disabling or rendering ineffective this torquing means under starting conditions, the duration and extent of the starting nutation of the instrument is reduced advantageously.

A further advantage attained by the improved starting arrangement is that the instrument is usable as a reference before the rotor is up to speed. A normal levelling torque added to the torque due to the reaction of the accelerating rotor during starting provides a levelling rate that is too high for the instrument to be used as a reference before the rotor has attained normal speed. This is because of the fact that an excessive levelling rate necessarily causes an excessive azimuth error during turns. With the present invention in which the normal levelling torque is reduced to null or substantially cut down at starting, the instrument is usable as a reference while the rotor is still accelerating. The improved arrangement is particularly advantageous in instances where a rotor is employed of the character that takes a relatively long time to-get up to speed.

Other advantages and novel features of the invention are hereinafter more particularly set forth in the description of the invention relative to the accompanying drawing in which,

. Fig. 1 is a side elevation of a gyroscopic instrument embodying the present inventive concepts. The housing of the instrument shown in Fig. l is in section as is a portion of the rotor frame;

. Fig. 2 is a circuit diagram showing the elements of the present invention arranged in a preferred relation;

Fig. 3 is a view similar to Fig. 2 showing a modified form of the invention; and

Fig. 4 is a curve showing the current-time characteristic of the rotor spinning motor of the arrangement during the starting period.

With reference to Fig. 1 of the drawing, a gyroscopic instrument of the directional gyro type is illustratively employed to show a practical embodiment of the present inventive concepts. An azimuth reference instrument of this character, as shown, includes a housing or casing ID that may provide a window H having a lubber line thereon (not shown) readable on a compass card l2 in accordance with conventional construction. The instrument is fixedly mounted on the craft on which it is used with the gimbal or vertical ring l3 within the housing I0 supported with freedom about a normally vertical axis. The rotor frame I4 is supported on the ring with freedom about a normally horizontal axis. Relative to the housing ID, the frame I4 is universally mounted with freedom about two mutually perpendicular axes. As shown in Fig. 1, the gyroscopic rotor i5 of the instrument is pivotally mounted in the frame H to spin about a horizontal axis that is normally perpendicular to both the axes of freedom of the frame; The card i 2 is shown as suitably fixed to the ring I3.

The electric motor for spinning the gyroscopic rotor l5 herein shown is a three phase A. C. induction motor whose wound stator is indicated at IT. The squirrel cage type rotor l8 of the spinning motor is included as a portion of the gyroscopic rotor l5.

This electric motor has the starting characteristic that the wound stator thereof draws a decreasing amount of electric current from the line as the gyroscopic rotor accelerates from a standstill condition to reach normal operating speed. As shown by the curve in Fig. 4, the current drawn from the line by the motor is at its maximum when the motor is first connected to the line by the closure of the starting switch 18. As the rotor picks up to speed, the current decreases with passage of time. With the rotor up to speed, the current levels off at a relatively low value of about one-tenth of that required during the motor accelerating period. Electric motors for spinning the gyroscopic rotor of an equivalent type to that described whose starting characteristics are the same may obviously be em-- ployed in carrying out the teaching of the present invention. The illustrated and described spinning motor per se is of well known construction in the motor art.

In accordance with the present invention, means are provided including motive means operable to exert a torque about an axis of the rotor frame l4 and in particular, in this instance, a levelling torque about the axis of ring l3. Such means may be of the character shown in U. S. Patent No. 2,381,438 of August 7, 1945, to R. S. Curry, Jr., in the form of a torque motor gener-- ally indicated at and a commutator and brush type selector switch generally indicated at 2|. The torque motor may be an A. C. induction motor of the squirrel cage type whose inductive rotor is fixed to the housing It) and whose polyphase wound stator is fixedly connected to the ring l3. Motor 20 operates to exert a torque about the axis of ring |3 to cause precession of the frame l4 about its normally horizontal axis on the ring l3 so that the spin axis of the rotor I5 is maintained horizontal. The selector switch 2| detects tilt of the frame |4 relative to the ring l3 and as shown in the above identified patent may include a commutator segment 23 fixed to the trunnion extending from the frame 4.4 and two brushes 24, 25 that are suitably fixed to the ring |.3. This type of switch 2| is also shown inFig. 2. In the arrangement shown, the switch 2| conducts electrical energy only when there is relative tilt between the frame and ring from a normal relation. Otherwise, the same breaks the circuit to the torque motor the brushes then engaging the insulating .area of the switch.

In the form of the invention shown in Fig. 2, one of the windings of the torque motor 2| is indicated at 26. This is connected by lead 2'! to brush 2.5 and by lead 28 to brush 24. The winding 25 is energized, .as shown, from a suitable source of electrical energy or A. 0. main 29 by way of switch l9, lead 30, and transformer 3| whose secondary winding is connected by lead 32 to segment 23 and by lead 33 to a center tap position on the winding .26. The return connection of the primary winding of the transformer 3| includes leads 34 and 35 to the switch I9 and main .29. Winding 26 of torque motor 2| is energized only when the frame 14 .is tilted relative to the ring |'3 and brushes 24 or 25 engage the conducting segment 23. Winding 36 of the torque motor 2| is normally energized from main 29 by way of switch l9, lead 31, lead .38, the armature 39 of a D. C. relay 40, contact 4|, lead 42, lead 43, the winding 36, and leads 34, 35 to the switch Hi to the main. In this form of the invention, a resistor 44 is arranged in the circuit to the Winding 36 in shunt relation to the armature .39 of the relay. Spring 45 of the relay normally maintains the armature 33 engaged with contact 4| so the resistor 44 in the circuit to the winding 35 is bypassed and the winding fully energized. When the armature 39 is out of engagement with the contact 4| as hereinafter described, the resistor 44 is situated in the circuit to the winding 36, the same operating to substantially decrease the energization thereof from the main. The winding 46 for the relay is controlled by the output of a rectifying bridge 4! that may be formed of four selenium rectifiers arranged as shown. The bridge 41 passes A. C. to lead 48 from lead 31. As shown in Fig. 2, the windings of the stator H of the spinning motor are energized from the main by way of switch l9 and leads 31, 48, lead 35 and lead 30.. Relay 40 in accordance with the present invention provides a means sensitive to the current drawn by the spinning motor of the instrument under starting conditions that operates to render the torque motor 2| ineffective while the rotor is accelerating. The relay is adjusted so that as long as the current is above that required for normal operation with the rotor up to speed, the field of the winding is sufiiciently strong to overcome the spring 45 and pull the armature 39 away from engagement with contact 4|. The shunted resistor 44 is now included in the circuit to the winding 36 of the torque motor. As soon as the rotor reaches normal operating speed and the current drawn by the spinning motor is at its normal value, spring 45 of the relay closes the armature 39 and contact 4| to shunt out resistor 44 so that the winding 36 is restored to normal operation. When the instrument is started from a stand-still condition by closing switch l9 to energize the spinning motor, the frame I4 is in a tilted condition relative to the ring I3 so that depending in the tilt there would be a continuous torque exerted in one direction about the axis of the ring if the torque motor were not rendered in effective or disabled. This torque adds to the starting nutation of the instrument and may lengthen the duration of the same considerably. By eliminating the torque under starting conditions the duration of nutation is appreciably decreased. The starting nutation of the instrument may be damped by means of a damping ring 43 which is a hollow circular tube filled with a damping fluid that is shown in Fig. l as fixedly mounted in concentric relation to the ring I3. In the arrangement shown, the ring is suitably fixed to the compass card I2. During the acceleration of the rotor of the instrument, a reaction torque due to the acceleration is present that operates in a direction to level the frame l4 relative to the ring l3. Such a torque if added to the normal levelling torque during the starting period provides a levelling rate that is too high for the instrument to be used as a reference if the craft using the instrument enters a turn or assumes a banked condition. By means of the present invention, the normal levelling torque means is rendered ineffective during the starting period, so that the instrument is usable as a reference even before the rotor gets up to its normal operating speed.

In the modified form of the invention shown in Fig. 3, an A. C. relay is substituted for the D. C. relay 40 and bridge .4! in Fig. 2. Also, the armature 5| and contact open the circuit including the winding 36 of torque motor 2| to disable the torque motor during the starting period. Relay 5|] is sensitive to the current drawn by the spinning motor from the line and does not reclose the torque motor circuit until the rotor from the instrument is spinning at normal speed and drawing the normal current from the line.

The tilt detecting switch for energizing winding 26 of torque exerting means 2| is shown in the form of a pair of conducting commutator segments 53, 54 and a pair of brushes 55, 55. Like switch 2|, the spaced segments are fixed to the trunnion of frame I4 and the brushes are fixed to the ring l3. Winding 26 is conected to brushes 55 and 55 by way of leads 5! and 59. Lead 58 connects segment 53 and lead 30. Energy is supplied from the line by way of auto transformer 60 connected across leads 35 and 30 by way of a tapped connection and lead 6| to the segment 54. With the brushes 55, 56 engaging the insulating spaces between the segments 53, 54, the switch is non-conducting and the winding 2.3 is not energized. With tilt of the parts from a normal condition, brush 55 contacts segment 53 or aosaeo'r 54 and brush 56 contacts segment 54, or 53 and the winding 26 is energized. The operation of this form of the invention is identical with that hereinbefore set forth in connection with Fig. 2 of the drawing.

Since many changes could be made in the above construction and many apparently widely diiTerent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a directional gyro having a ring mounted with freedom about a vertical axis, a rotor frame mounted on said ring with freedom about a horizontal axis and a gyroscopic rotor mounted in said frame; a starting arrangement including an electric motor for spinning said rotor of the character that draws a decreasing amount of electric current as the rotor accelerates from.-a.standstill condition to reach normal operating speed, means including motive means operable to exert a torque about the axis of the ring, and means. sensitive to the current drawn by the spinning motor operable to render said torque exerting means ineffective while the rotor is accelerating.

2. In a directional gyro having a ring'mounted with freedom about a vertical axis, a rotor frame mounted on said ring with freedom about a horizontal axis and a gyroscopic rotor mounted in said frame; a starting arrangement including an electric motor for spinning said rotor of the character that draws a decreasing amount of electric current as the rotor accelerates from a standstill condition to reach normal operating speed, means including motive means operable to exert a torque about the axis of the ring, and means sensitive to the current drawn by the spinning motor for disabling said torque exerting means until the rotor reaches normal operating speed.

3. In a directional gyro having a ring mounted with freedom about a vertical axis, a rotor frame mounted on said ring with freedom about a horizontal axis and a gyroscopic rotor mounted in said frame; a starting arrangement including an A. C. induction motor for spinning said rotor, means including an A. C. induction motor for exerting a torque about the axis of the ring, and current sensitive means for rendering said torque exerting motor inefi'ective while the current drawn by said spinning motor is above that required when the rotor is spinning at its normal operating speed.

4. In a directional gyro having a ring mounted with freedom about a vertical axis, a rotor frame mounted on said ring with freedom about a horizontal axis and a gyroscopic rotor mounted in said frame; a starting arrangement including an electric motor for spinning said rotor of the character that draws a decreasing amount of electric current as the rotor accelerates from a standstill condition to reach normal operating speed, means including an electric motor operable to exert a torque about the axis of the ring; a source of electrical energy, a circuit connecting said source and spinning motor, a circuit connecting said source and torque exerting motor, and means situated in the circuit to said spinning motor sensitive to the current therein for disabling said torque exerting motor circuit while the rotor is accelerating.

5. In a directional gyro having a ring mounted with freedom about a vertical axis, a rotor frame mounted on said ring with freedom about a horizontal axis and a gyroscopic rotor mounted in said frame; a starting arrangement including an A. C. induction motor for spinning said rotor, means including an A. C. induction motor operable to exert a torque about the axis of the ring, an A. C. source of electrical energy, a circuit connecting said source and spinning motor including a current sensitive relay having an armature, a circuit connecting said source and torque exerting motor including the armature of the relay and a shunting resistor, said relay operating by its armature to include the resistor in the circuit to the torque motor until the spinning motor has substantially reached its normal operating speed.

6. In a directional gyro having a ring mounted with freedom about a vertical axis, a rotor frame mounted on said ring with freedom about a horizontal axis and a gyroscopicrotor mounted in said frame; a starting arrangement including an A. C. induction motor for spinning said rotor, means including an A. C. induction motor operable to exert a torque about the axis of the ring, an A. C. source of electrical energy, a circuit connecting said source and spinning motor including a current sensitive relay having an armature, a circuit connecting said source and torque exerting motor including the armature of the relay and a shunting resistor, said relay operating by its armature to include the resistor in the circuit to the torque motor until the spinning motor has substantially reached its normal operating speed.

7. A starting arrangement for an electrically operated directional gyro instrument with a vertical ring comprising an A. C. induction, rotor spinning, motor; an A. C. induction motor for exerting a torque about the axis of the ring; an A. C. source; a circuit connecting said source and spinning motor including a relay having an armature; a circuit connecting said source and torque exerting motor including the armature of said relay; said relay operating by its armature to open the circuit to the torque motor until the spinning motor has substantially reached its normal operating speed.

8. An arrangement for reducing the starting nutation of an electrically operated gyroscopic instrument comprising a rotor spinning electric motor of the character that draws a decreasing amount of current as the motor accelerates from a standstill condition to reach normal operating speed, a levelling torque exerting electric motor, a source of electrical energy. a circuit connecting said source and spinning motor, a circuit connecting said source and torque exerting motor, and means sensitive to the current in the circuit of said spinning motor operable to render said torque exerting motor circuit ineffective until the spinning motor has substantially reached its normal operating speed.

' CLARE E. BARKALOW.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,589,039 Anschutz-Kaempfe June 15, 1926 2,441,307 Alkan May 11, 1948 FOREIGN PATENTS Number Country Date 102,197 Sweden July 29, 1941 

